It is believed that IUU fishing has escalated over the past 20 years, especially in the high seas, and is now estimated to amount to 11-26 million tonnes of fish harvested illicitly each year, worth between $10 and $23 billion.

Flag states are already required to maintain a record of their registered vessels together with information on their authorization to fish, such as the species they may fish for and the type of gear they may use. However, many fishing vessels engaged in illegal activities circumvent such control measures by "flag hopping" – repeatedly registering with new flag States to dodge detection, which undermines anti-IUU efforts.

The FAO Voluntary Guidelines for Flag State Performance spell out a range of actions that countries can take to ensure that vessels registered under their flags do not conduct IUU fishing, including monitoring, control and surveillance (MCS) activities, such as vessel monitoring systems (VMS) and observers. They promote information exchange and cooperation among countries so that flag states are in a position to refuse to register vessels that are "flag-hopping" by attempting to register with another flag state or to refuse vessels that have been reported for IUU fishing. The Guidelines also include recommendations on how countries can encourage compliance and take action against non-compliance by vessels, as well as on how to enhance international cooperation to assist developing countries to fulfil their flag state responsibilities. Although the guidelines are voluntary, their endorsement by the Twenty-first session of the FAO Committee on Fisheries (COFI), is a public signal by countries of their intent to adhere to a shared set of standards for flag state performance in the fight against IUU fishing activities.

A flag state is defined as any country– whether coastal or landlocked – that registers a fishing vessel and authorizes the vessel to fly its flag. The guidelines draw on and refer to existing international instruments such as the 1993 FAO Compliance Agreement, the 1995 FAO Code of Conduct for Responsible Fisheries and the 2001 FAO International Plan of Action to Prevent, Deter and Eliminate IUU fishing.